4d-Metal Ion Ru3+-Incorporation in Prussian Blue Analogue-Derived Anodic NiFe(O)OH and Cathodic NiFe(OH)2 Nanosheets Promotes Electrochemical Seawater Splitting

Electrochemical seawater splitting is a potential approach to producing H2 and O2. As seawater contains different cations and anions, the direct electrochemical splitting of seawater suffers from various challenges like chlorine evolution, corrosion of electrodes, and poor stability for the catalysts. Herein, we have demonstrated the incorporation of 4d-metal ion Ru3+ in Prussian blue analogue-derived Ru–NiFe(O)OH (at the anode) and Ru–NiFe(OH)2 (at the cathode) nanosheets for electrochemical seawater splitting. The introduction of Ru3+ into the active catalysts modulated the electronic structure to improve the cell voltage, reaction kinetics, and stability for seawater splitting. In real seawater, the anodically reconstructed Ru–NiFe(O)OH nanosheets reached 50 mA cm–2 current density at a 260 mV overpotential for oxygen evolution, while Ru–NiFe(OH)2 at the cathode attained −50 mA cm–2 current density for hydrogen evolution at only an 83 mV overpotential. The coupling of Ru–NiFe(O)OH and Ru–NiFe(OH)2 nanosheets as the anode and cathode, respectively, produced 50 mA cm–2 current density at a cell voltage of 1.58 V for overall seawater splitting, outperforming the RuO2∥Pt/C catalyst. Moreover, 100 h stability was also achieved for the overall seawater splitting.